Thermally responsive electrical switch with overstress protection means



llg- 3l, 1965 H. J. MGCARRICK ETAL 3,204,065

THERMALLY RESPONSIVE ELECTRICAL SWITCH WITH OVERSTRES S PROTECTION MEANS 2 Sheets-Sheet l Filed Jan. 2, 1965 (C4/ur /v j .5A/Vrana, y Arr Aug. 3l, 1965 H. J. MccARRlcK ETAL 3,204,065

THERMALLY RESPONSIVE ELECTRICAL SWITCH WITH OVERSTRESS PROTECTION MEANS 2 Sheets-Sheet 2 Filed Jan. 2, 1965 ww mw N\ QS HJG@ United States Patent O 3,204,065 THERMALLY RESPONSIVE ELECTRICAL SWITCH WITH OVERSTRESS PROTECTION MEANS Henry J. McCarrick, Middleboro, and Harry E. Shaw, Seekonk, Mass., and Carlton E. Sanford, Riverside, RJ., assignors to Texas Instruments Incorporated,

Dallas, Tex., a corporation of Delaware Filed Jan. 2, 1963, Ser. No. 249,021 9 Claims. (Cl. 200-137) This invention relates to thermally responsive electrical switches and with regard to certain more specic features, to a snap-acting, probe-'type thermally responsive switch.

Among the several objects of the invention may be noted the provision of a novel and improved probe-type or immersion-type thermally responsive snap-acting electrical switch; the provision of such switches which are particularly suited for miniaturization and can be provided in diminutive tubular yor lance-like form adapted conveniently to be inserted into t-he small spaces directly adjacent the heating parts of motors, transormers, iluorescent light ba-llasts yand the like, to which heating parts a temperature response is to be made by the switch; the provision of a switch lhaving a snap-acting element and means for preventing overstressing of the element when the switch is subjected to large or radical temperature changes which may cause over-ride or under-ride conditions; the provision of a switch of the class descri-bed which has good vibration resistance and which is adjustable for operation `over a relatively -wide range of ternperatures; lthe provision of such a switch which can be conveniently provided in hermetically seal-ed form; and the provision of a switch of the class described which is relatively simple in construction and is low-cost to assemble and manufacture.

Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combina-tions of element-s, features of construction,` and arrangements of parts which will be -exemplied in the structures hereinafter described, and the scope of the application of Which will be indicated in the following claims.

In the accompanying drawings, in which one of the various possible embodiments of the invention is illustrated:

FIG. l iis a top plan view of a switch according to one form lof the invention with parts of the switch casing broken away for clarity of illustration;

FIG. 2 is `an enlarged fragment-ary elevational view of the switch shown in FIG. l, showing the parts in a contacts-closed position and with other parts broken away for clarity of illustration;

FIG. 3 is a bottom plan view of the switch shown in FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view taken on line 4-4 of lFIG. 1 showing the parts in a contactsopen position;

lFIG. 5 is a sectional view `talcen on line 5-5 of FIG. 2;

FIG. 6 is a sectional view taken online 6 6 of FIG. 2; and

FIG, 7 is a fragment-ary perspective view of a portion 4of the force shunting fra-me member forming part of the switch shown in FIG. 1.

ACorresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Dimensions of certain of the parts as shown in the drawings may `have been modified and/tor exaggerated for purposes of clarity of illustration. t

3,204,065 Patented Aug. 31, 1,9165

ICC

Referring now more particularly to FIG. 1, there is shown .a thermally responsive switch according to the present invention yand indicated generally at 10. Switch 10 includes a tubular, lance-like housing 12 formed of a material preferably of the type having a relatively high co-eflicient of thermal expansion such as, for example, brass or stainless steel. Telescopically disposed within tube 12 is a rod-like member 14 formed of a material preferably of the ty=pe having a relatively low co-eicient of thermal expansion such as Invar, for example. One end of rod 14 is secured to the closed-end portion of tube 12 as by welding as at 16 as best seen in FIG. l. The other end of rod 1'4 terminates in a relatively at platelike support portion 18.

Switch 10 includes a snap-acting motion translating land amplifying element generally referred to by numeral 20. Element 20 is ully described in a copending `application entitled Motion Translating andAmplifying Devices, application Serial No. 249,094, led January 2, 1963, inthe name of Henry J. McCarrick, and assigned to the assignee of the instant application, to which reference may be had for details of construction and operation of element 20.

Element 20 includes an integrally formed pair of outer arms 22 and 24, a pair of inner arms 26 and 28, and an inner tongue 30 integrally interconnected adjacent one end thereof to inner arms 26 and 28 by a junction portion 312. The right hand ends (as seen in FIG. 1) of outer 'arms 22 and 24 are integrally connected to an anchoring tab 34. The left hand ends of outer arms 22 and 24 are each respectively liexi-bly and integrally connected to the left hand end of arespective one of inner arms 28 and 26 ,and also to an actuating member 40 which extends beyond the left `hand end 42 of innerY tongue 30. Actuator member 40 is electrically connected and mounts an electrical Iconta-ctl 44 adjacent its free end as best seen in FIGS. 2 and 4.

The open end 50 of tube 12 is closed and 'hermetically sealed by a lian-ged glassJto-metal header assembly generally indicated at `52. Assembly 52 includes a metal ring 54 having an annular-ly extending llange 56 which is secured t-o a corresponding ange 58 provided by tube 12 las by welding as at 60. Meta-1 ring 54 may be formed, for example, of stainless steeland provides an aperture f62`(see FIG. 4) in which is telescopically disposed a terminal pin 64. Terminal pin 64 is mounted and maintained in electrically insulated relation with respect t0 ring 54 by means 'of .a glass sealant 66 which, as best seen in FIG. 4, extends axially along a substantial portion of the length of terminal pin `64 within urbe 12 so as to electrically isolate the terminal pin from other parts of the switch which will be described in greater detail below. The switch as illustrated in FIGS. 1-4 is of a groundedtype construction i`n which the tubel12 is electrically conducting. An electrically conductive terminal member 70 is electrically connected to flange 56 as by welding as at 72, as best seen in FIGS. 2 and 4.`

Switch 10 includes an angle shaped adjustment lever, a member generally indicated at 80, and comprising a short leg 82 and a long leg 84. Adjusting lever member 80 is formed of a good electrically conductive spring material such as AISI type number 403 stainless steel. Short leg 82 is electrically connected and iixedly secured to metal ring 54 as by welding at 86. Long leg 84 provides an oval-shaped enlarged opening 88 for reception of terminal pin 64 and the surrounding portion ofthe glass sealant 66. Leg 84 includes a notched struck-out portion 90 which extends leftwardly as seen in FIGS. 2 and 4. Struck-out tab 90 provides a rectangular keyhole shaped opening 92 in leg 84, the wider portion of the opening being lowermost as-seen in FIG. 4. Y

Switch further includes a force shunting frame member generally indicated at numeral 100 which was initially in the form of a at sheet which has been punched and formed to provide a finished one-piece frame member symmetrical in shape relative to its longitudinal centerline. Frame member 100 is formed of a good electrically conductive material which also provides substantial strength such as, for example, a nickel alloy. Frame 100 includes an elongated rectangular opening 102, longitudinally extending stiltening and reenforcing ribs 104 and 106, a struck-out and bent angle member having a short leg 108, and a U-shaped long leg 110 which provides an enlarged window opening 112 therethrough (as best seen in FIGS. 4 and 7) which registers with opening 88 to loosely receive therethrough, terminal 64 and the surrounding glass sealant 66 as best seen in FIG. 4, and a portion of another frame member 140 to be described below. Legs 108 and 110 constitute an overtravel lever the function and operation of which will be described in greater detail below. Frame 100 also includes a leftwardly projecting (see FIGS. 4 and 7) tab portion 116 notched as at 118 and 120 to respectively provide spaced pairs of opposed abutting surfaces 122, 124, 126 and 128 as best seen in FIG. 7. Shorter leg 108 is xedly secured and electrically connected to leg 82 of member 80 as by welding as at 109 and spaces leg 110 from leg 84 to permit relative pivotal movement of leg 110 with respect to leg 84 about the junction between legs 108 and 110. Tab or tongue 116 has a width slightly less than the widest keyhole portion of the slot 92 in leg 84, and is received therethrough so that notches 118 and 120 are disposed in the narrow portion of the slot 92 and receive portions of leg 84 therein. The spacing between opposed pairs of abutting walls 122, 124 and 126, 128 is sufficiently greater than the thickness of leg 84 to permit relative movement between trarne 100 and adjusting lever leg 84, to provide a lost motion connection therebetween as best seen in FIGS. 3 and 6.

Frame 140 is rectangular shaped and is in the form of a flat plate having a rectangular shaped opening 142 therein in registry with opening 102 of frame 100 to receive actuator 40 for movement therethrough. Frame 140 also has a leitwardly projecting tab portion 144 (as seen in FIGS. 2 and 4) which extends through openings 112 and 92 and is ixedly secured to tab 90 of adjustment lever 80 as by welding as at 146. This lixes frame 140 to lever 80 for movement therewith as a unit. Frame member 148 is formed of a good electrically conductive material such as a nickel alloy, for example.

Referring now to FIG. 1, end 42 of tongue 30* of element is electrically connected and secured or anchored to frame 140 as by welding as at 130. Tab 34 is anchored and electrically connected to support end 18 of rod 14 as by welding as at 35. End 18 is also xedly connected to the right-hand end of frame member 100 as by welding at 19. A U-shaped member 160 formed of electrically conductive contact material such as a silver alloy, for example, is iixedly secured and electrically connected to the free inner end of terminal pin 64 as by welding at 158.

Member 160 projects through openings 142 and 102 and provides an electrically conductive contact 162 positioned for engagement with contact 44 carried by actuator arm 40 of element 20. The upper leg 166 of the U-shaped member 160 is covered with an electrically insulating material 170, such as for example, a ceramic, to prevent short circuiting when actuator arm 40 snaps to separate contacts 44 and 162.

Operation of switch 10 as thus far described is as follows: It will be clear that when rod 14 and tube 12 are exposed to changes in temperature conditions (c g., an increase) that differential expansion will result in relative movement between these parts in a manner Well-known in the art. This diierential expansion also causes end 18 of rod 14 (which acts as one of the supports for element 20) to move relative to the supporting frame 140 (to which inner tongue is secured) to effect snapacting or overcentering of element 20. On an increase in temperature support 18 will move to the right as seen in FIGS. l, 2 and 4, and in a direction away from supporting frame to eiect snap-acting or overcentering of element 20 to snap actuator arm 40 from the Contactsclosed position shown in FIG. 2, to the contacts-open position shown in FIG. 4, in which actuator arm 40 abuts electrical insulating material 170. It Will be understood that movement of supporting end 18 to the right (as seen in FIG. 1) in response to temperature increase, exerts a pulling force on snap-acting element 20 which stresses parts 22, 24 and 30 in tension and stresses parts 26 and 28 in compression. Upon a decrease in temperature, contraction occurs and end 18 will move to the left as seen in FIG. 1 to relieve or reduce stresses in parts 22, 24, 26, 28 and 30 of element 20. Return from the FIG. 4 to the FIG. 2 position occurs with snap action when support 18 moves back a predetermined amount toward frame support 140 upon a decrease in temperature.

Switch 10 further includes adjusting means in the form of a screw received in a threaded aperture 182 provided by ring 54. The outer end of screw 180 is provided with a notched portion 186 for reception of a suitable tool to eiiect rotation thereof and the inner end 184 abuts spring leg 84 of adjusting lever 80. It will be seen from FIGS, 2 and 4 that rotation of screw 180 to move the latter to the right will force leg 84 of adjustment lever spring member 80 to rotate counter-clockwise about its junction with leg 82 and will cause frame member 140 (which is xedly connected with the member 80 as at 146) to move to the right to vary the initial stress in snapacting element 20 and thereby vary the amount of actuating displacement (between supports 18 and 140) required to eliect snapping. This in turn influences the temperature at which switch It) will operate or respond. Spring leg 84 is biased for movement in a clockwise direction (as seen in FIGS. 2 and 4) so as to at all times be biased for moving toward engagement with end 184 of screw 80.

The switch according to the present invention also provides means to protect the relatively trail or delicate and usually miniaturized snap-acting blade 20 from becoming over-stressed on under-ride and over-ride conditions. By an under-ride or undertravel conidtion is meant relative movement between parts which results on contraction of parts (due to decreasing temperature conditions) which causes support end 18 to continue t-o move to the left (as seen in FIGS. l, 2 and 4) after blade 20 has snapped from the contacts-open FIG. 4 position to the contacts-closed FIG. 2 position. By overtravel or over-ride condition is is meant relative movement between parts which results from expansion of parts (due to increasing temperature conditions) which causes continued movement of support end 18 to the right (as seen in FIGS. l, 2 and 4) after blade 20 has snapped from the FIG. 2 (contacts-closed) to the FIG. 4 (contacts-open) position. Such continued movement of support 18 after snapping of element 20 could result in undesirafbly over-stressing element 20. The present invention provides means for protecting and preventing element 20 from becoming deleteriously overstressed both on over-ride and on under-ride.

If an overtravel condition occurs as a result of an increase in the temperature conditions to which switch 10 is subjected, i.e., continued movement of support 18 to the right (as seen in FIGS. 1, 2 and 4) after snapping of element 20 to the contacts-open FIG. 4 position will continue to further stress element 20 and to move frame 100 to the right until the latter has moved far enough to the right so that abutting surfaces 122 and 128 of frame tab 116 engage leg 84 of the adjusting lever. Thereafter continued movement of support end 18 to the right (as seen in FIGS. l, 2 and 4) will cause frames 108 and 140' to move together as a unit to the right which results in maintaining t'he spacing of supports 140 and 18 constant and prevents any further stressing of the blade 20. It will be understood that the unitary movement to the right of frames 100 and 140 which occurs after engagement of abutting surfaces 122 and 128 wi-th leg 84 takes place because frame 140 is fixed to leg 84 (through tabs 144 and 90) and frame 100 abuts leg 84 for movement to the right. Continued further movement to the right will cause leg 84 to rotate in a counterclockwise direction (as seen in FIGS. 2 and 4)'about its junction with leg 82. 0n cooling, contraction of the parts results in moving support 18 and frames 100 and 140 to the left to reduce the forces exerted against element 20 after leg 84 moves back into engagement'wit-h screw 180. Element 20 will not snap back or return to the FIG. 2 contacts-closed position until after leg 84 has rotated (under its inherent spring bias) in a clockwise direction into engagement with tip 184 of adjusting screw 180. Thereafter continued leftward movement of support 18 on cooling will cause blade 20 to snapfromthe FIG. 4 contacts-open to the FIG. 2 contacts-closed position. Continued leftward movement of suppor-t 18 after element 20 has snapped to the FIG. 2 contacts-closed position, will continue to further stress the element 20 and will also cause movement -of frame 100 to the left (as seen in FIG. 2) until abutting surfaces 124 and 126 respectively of notches 120 and 118 of frame tab 116 abut leg 84. Thereafter, further movement oflframe 100 and support 18 to the left (as seen in FIG. 2) on continued cooling will be resisted by leg 84 through its abutting engagement with screw 180'. This stabilizes or maintains constant the spacing between element support 18 and 140 and on further contraction under continued sustained cooling conditions also protects and prevents any further stressing of the blade or element 20. Thereafter the stresses resulting from further contraction of parts on cooling will be transmitted or shunted (away from element 20) by frame 100 to rod 14 to stress the latter in compression. lt will be understood that rod 14 is a relatively sturdy member which is eminently better suited for withstanding the stress developed during under-ride conditions than is the comparatively frail blade 20. The stitening ribs 104 and 106 of frame 100 serve to reinforce the frame to enable it to better withstand the compressive forces developed on underride conditions and for transmitting these forces to the rod 14.

It will be understood that during movement of the frame 100 relative to leg 84, Ibent leg 110 rotates about its junction with leg 108, the former being initially spaced far enough away from leg 84 to permit this rotation.

The adjustment features and temperature over-ride and under-ride protection provided for snap-acting element 20 by the present invention have the advantages of permitting construction of a thermally responsive switch in miniaturized form which can accurately operate over wide ranges in temperature without deleterious changes in calibration, and which have good vibration resistance. Switches have been produced according to this invention which can operate over temperatures ranging from minus 40 C. through 200 C. without deleterious changes in calibration. Hermetically sealed switches according to lthe present invention have also been made as small as 0.285 in height, 0.395 in width and slightly over 2.5 in length (excluding the extent of terminals 64 and 70) and have been able to withstand as much as G acceleration at 120 cycles per second without encountering contact chatter.

If desired, switch 10 may be encased in an electrically insulating sleeve, for example, such as Mylar. If desired, a non-grounded construction can be provided by electrically insulating adjusting lever 80 from adjusting screw 180 and from header ring 54 and also by electrically insulating force shunting frame 100 and blade 20 from support end 18 of rod 14.

Although having more general uses, 4the switch according to the present invention is particularly useful for motor protection and because Iof its small size and lance-like construction is particularly suited for insertion within the motor windings to advantageously sense winding temperatures directly.

In view of the above it will be seen that the several objects of the invention Vare achieved and other advantageous results attained.`

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, 'and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

We claim:

1. A thermally responsive electrical switch comprising a snapacting element; a pair of electrical contacts, said element being operatively connected with one of `said contacts for movement of the latter into and out of engagement with the other of said contact-s; a housing; first and second frame members in said housing each connected to a respective one of a pair of spaced portions of said element; limiting means connected with said housing; said limiting means comprising a lever member mounted on said housing for pivotal movement relative thereto; said first frame member being fixed to said limiting means for movement in unison therewith; said second frame member being interconnected with said limiting means for movement relative thereto and for movement in unison therewith in at least one direction after a predetermined amount of relative movement therebetween; the portion of said element connected with said first frame and Said first frame being interconnected with thermally responsive means for causing relative movement between said first and second frames in response to temperature change to stress said element to cause snapping thereof and actuation of said contacts; said limiting means cooperating with said first and second frames to limit relative movement between said frames in at least one direction after snapping of said element to prevent overstressing of said element.

2. The switch as set forth in claim 1 and including an adjustably mounted member engaging said lever member for moving said member to calibrate said element; `and said lever member being biased for movement toward engagement with said adjustably mounted member.

3, The switch as set forth in claim 2 an-d wherein said lever member comprises an angle shaped member having a short and a long leg; said short leg being connected with said housing and said long leg being iixedly connected to said rst frame member; said long leg providing an aperture in which is received a projecting tab connected with said second frame to provide a lost motion connection between said second frame and said long leg.

4. The switch as set forth in claim 1 and wherein said thermally responsive means comprises a rod and tube having dissimilar coeicients of thermal expansion; said rod being connected adjacent one end thereof with said element and first frame; and said tube forming part of said housing.

5. The switch as set forth in claim 4 and wherein said tube has an open and a closed end; said rod being telescopically disposed within said tube and connected at its other end to said closed end of said tube; and means closing the open end of said tube.

6. The switch as set forth in claim 4 and wherein said tube has an open and a closed end; said rod being telescopically disposed within said tube and connected at its other end to said closed end of said tube; the open end of the tube being hermetically sealed by a glass-tometal header secured to said tube; and said lever member being secured to said header.

7. The switch as set forth in claim 6 and wherein lsaid header mounts Ia terminal pin in electrically insulated relation to said header and tube; said terminal pin mounting said other of said electrical contacts and said element being electrically connected to and mounting said one of said electrical contacts.

8. The switch as set forth in claim 6 and including an adjusting screw threadably mounted in said header and having a portion accessible exteriorly of said switch and another portion engaging said lever member for movement of said lever member and rst frame member in unison for Calibrating said element; and said lever member being spring biased for movement toward engagement with said adjusting screw.

9. A condition responsive switch comprising a snapacting element; a pair of electrical contacts, said element being operatively connected with one of said contacts for movement of the latter into and out of engagement with the other of said contacts; a housing; rst and second frame members, each connected to a respective one of a pair of spaced portions of said element; limiting means connected with said housing; said limiting means comprising a lever member mounted for pivotal movement relative to said housing to limit relative movement therebetween; said rst frame member being fixed to said limiting means for movement in unison therewith; said second frame member being interconnected with said limiting means for movement relative thereto and for movement in unison therewith in at least one `direction after a predetermined amount of relative movement therebetween; the portion of said element connected with said rst frame and said first frame being interconnected with condition responsive means for causing relative movement between said rst and second frames in response to predetermined changes in condition to stress said element to cause snapping thereof and actuation of said contacts; said limiting means co-operating with said rst and second frames to limit relative movement between said frames in at least one direction after snapping of said element to prevent overstressing of said element.

References Cited by the Examiner UNITED STATES PATENTS 2,734,968 2/56 Cooper 200-137 FOREIGN PATENTS 846,134 8/60 Great Britain.

25 BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner. 

1. A THERMALLY RESPONSIVE ELECTRICAL SWITCH COMPRISING A SNAP-ACTING ELEMENT; A PAIR OF ELECTRICAL CONTACTS, SAID ELEMENTS BEING OPERATIVELY CONNECTED WITH ONE OF SAID CONTACTS FOR MOVEMENT OF THE LATTER INTO AND OUT OF ENGAGEMENT WITH THE OTHER OF SAID CONTACTS; A HOUSING; FIRST AND SECOND FRAME MEMBERS IN SAID HOUSING EACH CONNECTED TO A RESPECTIVE ONE OF A PAIR OF SPACED PORTIONS OF SAID ELEMENT; LIMITING MEANS CONNECTED WITH SAID HOUSING; SAID LIMITING MEANS COMPRISING A LEVER MEMBER MOUNTED ON SAID HOUSING FOR PIVOTAL MOVEMENT RELATIVE THERETO; SAID FIRST FRAME MEMBER BEING FIXED TO SAID LIMITING MEANS FOR MOVEMENT IN UNISON THEREWITH; SAID SECOND FRAME MEMBER BEING INTERCONNECTED WITH SAID LIMITING MEANS FOR MOVEMENT RELATIVE THERETO AND FOR MOVEMENT IN UNISON THEREWITH IN AT LEAST ONE DIRECTION AFTER A PREDETERMINED AMOUNT OF RELATIVE MOVEMENT THEREBETWEEN; 